Evolution of the response of the CMS ECAL and possible design options for calorimetry at the High Luminosity LHC.

The performance of the CMS electromagnetic calorimeter (ECAL) has been continuously monitored at the LHC. The evolution of this performance is a critical issue for the future. Work has started to assess the need for possible changes to the detector to ensure adequate performance for High-Luminosity LHC (HL-LHC) operation which is planned for 2022 and beyond. In this paper, results from CMS running, beam tests and laboratory measurements on proton-irradiated crystals are combined to predict the performance of the current detector at the HL-LHC. In addition, various R and D studies are presented in case modification or replacement of the ECAL Endcaps is needed for the HL-LHC period.